The present invention relates to a liquid droplet ejection device, and more particularly, to a piezoelectric actuator deformable to change an internal volume of an liquid chamber, such as an ink chamber of an ink jet printer head.
A liquid droplet ejection device is conventionally used as a printer head of an ink jet type printer. In such type of the printer head, a plate like piezoelectric plate member is provided as a part of a wall of an ink chamber. Upon application of a drive voltage to the piezoelectric plate member, the wall is deformed to induce pressure waves to the ink contained in the ink chamber. Thus, ink can be ejected out of a nozzle in communication with the ink chamber.
In order to sufficiently deform the wall portion for providing sufficient ink ejection, high driving voltage is required. However, application of high driving voltage is detrimental to energy consumption.
It is an object of the present invention to overcome the above-described problem and to provide an energy saving liquid droplet ejection device capable of providing a sufficient deformation of the piezoelectric plate member even at a low driving voltage.
This and other objects of the present invention will be attained by a piezoelectric actuator including an improved piezoelectric plate member and electrodes. The piezoelectric plate member is formed of a piezoelectric material and has a first surface and a second surface opposite to the first surface in a thickness direction of the piezoelectric plate member. The piezoelectric plate member is fixed at fixed positions spaced away from each other in an extending direction of the piezoelectric plate member. The electrodes are adapted for deforming the piezoelectric plate member. Each electrode is positioned for imparting an electric field to the piezoelectric plate member so as to expand a part of the piezoelectric plate member in the extending direction, the part being defined between neighboring fixed positions of the piezoelectric plate member. A vacant zone is positioned at a position deviating to one of the first and second surfaces at a position between the neighboring fixed positions. Expansion force of the part of the piezoelectric plate member in the extending direction causes the part to be bendingly deformed between the neighboring fixed positions.
In another aspect of the invention, there is provided a liquid droplet ejection device including the piezoelectric actuator and a liquid chamber constituting member defining a liquid chamber in cooperation with the part of the piezoelectric plate member. Each fixed position is positioned adjacent to a contour of the liquid chamber. Deformation of the part of the piezoelectric plate member provides a volumetric change of the liquid chamber.
In still another aspect of the invention, there is provided a piezoelectric ink jet printer head including a piezoelectric plate member, an ink chamber plate, a nozzle plate and electrodes. The piezoelectric plate member is formed from a piezoelectric material and has a first surface and a second surface opposite to the first surface in a thickness direction of the piezoelectric plate member. The piezoelectric plate member extends in an extending direction. The ink chamber plate is positioned directly below the piezoelectric plate member, and is formed with a plurality of holes arrayed in the extending direction. The piezoelectric plate member is fixed to solid portions of the ink chamber plate other than the holes. The nozzle plate is positioned below the ink chamber plate and is formed with a plurality of nozzles arrayed in the extending direction and positioned in alignment with the holes. A combination of the piezoelectric plate member, the ink chamber plate and the nozzle plate defines a plurality of ink chambers arrayed in the extending direction. The electrodes are adapted for deforming the piezoelectric plate member. Each electrode is positioned for imparting an electric field to the piezoelectric plate member so as to expand a part of the piezoelectric plate member in the extending direction, the part being defined in confrontation with the ink chamber. Vacant zones are positioned at positions deviating to one of the first and second surfaces and each vacant zone is positioned within an area of each hole. Expansion force of the part of the piezoelectric plate member in the extending direction causes the part of the piezoelectric plate member to be bendingly deformed toward or away from the ink chamber.